Abstract
To study effects of age on alpha adrenergic activation of aortic smooth muscle without complicating influences of anesthesia and recent surgery, 9 adult, 7 newborn (2-3 days) and 5 near term fetal sheep were instrumented with pressure and ultrasonic dimension gauges for measurement of aortic pressure and diameter and calculation of wall stress(σ) in the proximal third of the descending thoracic aorta. After recovery from surgery the conscious animals received methoxamine to stimulate aortic smooth muscle. Methoxamine, 50 μg/kg/min i.v., shifted σ-radius relationships in the adults towards a higher σ at any given radius (Δσ = 3.50 ± 0.40 × 105 dynes/cm2, p < .01). This shift in σ-radius relationship was not observed with twice the above dose of methoxamine in newborns (Δσ = 0.75 ± 0.19 × 105 dynes/cm2) or four times the dose in the fetus (0.82 ± 0.54 × 105 dynes/cm2). Additionally the effects of alpha adrenergic stimulation on arterioles were studied with i.v. methoxamine, 200 μg/kg, in 5 unanesthetized adults and newborns, previously instrumented with electromagnetic flow probes on the ascending aorta. Total peripheral resistance increased in the adult more than in the newborn (524 ± 46% and 169 ± 39% respectively, p < .01). Thus vascular smooth muscle responses to alpha adrenergic stimulation, as reflected by aortic σ-radius relationships and systemic vasoconstriction, are significantly greater in conscious adult sheep than in fetal or neonatal lambs.
Article PDF
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Pagani, M., Baig, H., Mirsky, I. et al. 143 REDUCED ALPHA ADRENERGIC RESPONSIVENESS OF FETAL AND NEONATAL AORTIC SMOOTH MUSCLE IN UNANESTHETIZED SHEEP. Pediatr Res 12 (Suppl 4), 387 (1978). https://doi.org/10.1203/00006450-197804001-00148
Issue Date:
DOI: https://doi.org/10.1203/00006450-197804001-00148